: In general, studies of modernization provide a context for studying adult-onset chronic disease and the plasticity of human form and function under the contrasting traditional and modern lifestyles found in modernizing populations (1). Specifically, modernization studies demonstrate the significant environmental context underlying population-level differences in these traits and conditions. An important elaboration of this environmental context is reflected in recent studies on fetal programming, in which nutritional stress during early development potentially increases the risk of obesity, adult-onset diabetes (NIDDM) and other chronic diseases later in life (2,3). It has become increasing clear that insulin function, especially insulin sensitivity, serves as a significant phenotypic link between fetal outcome (i.e. birth weight), obesity and adult-onset chronic disease (2,4). This proposal will investigate how birth weight and nutritional patterns influence insulin sensitivity and body composition during development. The Pacific island population of Western Samoan will serve as a natural experimental model for this project. (1). This population exhibits the contrasting nutritional patterns (traditional vs. modern) formed under the forces of modernization, and the contrasting body composition (e.g. height and weight) and prevalence rates of chronic disease consistently associated with this lifestyle dichotomization (5,6).